title: High cooperativity in coupled microwave resonator ferrimagnetic insulator hybrids.
abstract: We report the observation of strong coupling between the exchange-coupled spins in a gallium-doped yttrium iron garnet and a superconducting coplanar microwave resonator made from Nb. The measured coupling rate of 450 MHz is proportional to the square root of the number of exchange-coupled spins and well exceeds the loss rate of 50 MHz of the spin system. This demonstrates that exchange-coupled systems are suitable for cavity quantum electrodynamics experiments, while allowing high integration densities due to their spin densities of the order of one Bohr magneton per atom. Our results furthermore show, that experiments with multiple exchange-coupled spin systems interacting via a single resonator are within reach.
authors.affiliation: Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching, Germany.
authors.forename: Hans
authors.initials: H
authors.lastname: Huebl
authors.forename: Christoph W
authors.initials: CW
authors.lastname: Zollitsch
authors.forename: Johannes
authors.initials: J
authors.lastname: Lotze
authors.forename: Fredrik
authors.initials: F
authors.lastname: Hocke
authors.forename: Moritz
authors.initials: M
authors.lastname: Greifenstein
authors.forename: Achim
authors.initials: A
authors.lastname: Marx
authors.forename: Rudolf
authors.initials: R
authors.lastname: Gross
authors.forename: Sebastian T B
authors.initials: ST
authors.lastname: Goennenwein